JP5030753B2 - Pneumatic tire - Google Patents

Description

The present invention relates to a pneumatic tire with reduced air column resonance caused by circumferential main grooves formed in a tread pattern of the tire.
Further, the present invention relates to a pneumatic tire that can obtain good steering stability even in a vehicle having a high center of gravity, such as a passenger vehicle (hereinafter referred to as a minivan), which has increased in recent years.

  With the recent quietness of vehicles, the proportion of tire noise in automobile noise has become relatively large, so reducing tire noise has become a major issue. Above all, tire noise around 1000 Hz, which is easily heard by humans, is a major factor of noise outside the vehicle, and an immediate countermeasure is desired from the viewpoint of environmental problems.

By the way, tire noise belonging to a frequency band of about 800 to 1400 Hz is generated by so-called air column resonance, in which the air column defined by the circumferential main groove formed in the tread and the road surface resonates within the tire contact surface. It is generally known to do.
That is, in the state where the tire having the circumferential main groove is grounded, a pipe having the same length as the ground contact length is formed between the groove wall of the circumferential main groove and the grounding surface. As a result of repeated compression and release of air in the tube, noise called air column resonance is generated. The frequency f ₀ of the air column resonance sound has a sound velocity v, the length of the tube, that is, the length of the circumferential main groove L,
f ₀ = v / 2L
It is a constant frequency represented by

  In order to suppress such air column resonance, as shown in FIG. 3, Patent Document 1 reduces the air column resonance sound of a tire while maintaining steering stability while suppressing a decrease in wet performance. As a thing, the tread 1 is provided with two or more circumferential main grooves 2 and 3 that are continuous in a linear or zigzag shape in the circumferential direction, and at least one circumferential main groove (in FIG. 3, the circumferential main groove 2). ), A plurality of axial sub-grooves 5 having one end opened in the circumferential main groove and the other end ending in the land portion, and each axial sub-groove 5 is always 1 in the ground plane. There has been proposed a tread pattern in which an arrangement that completely includes the book is included.

Thus, by providing the sub-groove branched from the circumferential main groove, the frequency of the air column resonance can be dispersed. When the frequency is dispersed, it feels that the sound on the ear has softened and quieted, and this effect is called white noise.
The frequency dispersion effect varies depending on the shape of the sub-groove. Specifically, if the length of the sub-groove is l and the speed of sound is v, the frequency f of the newly generated sound that is dispersed is
f = (2n−1) × v / 4l
n: vibration order (n = 1, 3, 5...)
It is known that

  As another conventional technique for suppressing air column resonance, Patent Document 2 discloses a first sub-groove 29 opened in the circumferential main groove 22 and a circumferential main groove 24 as shown in FIG. There has been proposed a pneumatic tire in which a second sub-groove 30 that is open at a position is arranged. The first and second sub-grooves have a configuration in which a cross-sectional area increases from the opening end side to the circumferential main groove toward the terminal end side in the land portion, thereby reducing the sound pressure level of the air column resonance sound. Reduced.

  In Patent Document 3, rubber with high hardness is arranged on the outside of the vehicle, and rubber with low hardness is installed on the inside of the vehicle, so that wear resistance and steering stability are improved even in a vehicle with a high center of gravity. Techniques have been shown to reduce rolling resistance while maintaining.

  Patent Document 4 discloses a technique for improving steering stability at a small rudder angle by combining an asymmetric cross-sectional shape and an asymmetric pattern.

International Publication No. 2004/1037737 Pamphlet International Publication No. 2007/072824 Pamphlet JP 2003-326917 A JP 2007-15596 A

In the pneumatic tire described in Patent Document 1 described above, the frequency of the air column resonance generated in the circumferential main groove is dispersed by the axial sub-groove that is continuous with the circumferential main groove, and white noise is generated. It becomes possible. However, there are still the following issues to further enhance the effect of this technology.
In the pneumatic tire described in Patent Document 1, the ribs 12 sandwiched between the circumferential main grooves 2 and 3 are formed on the auxiliary grooves 5 as shown in FIG. It is divided by the groove 5. Thereby, since the rigidity of the portion of the rib 12 sandwiched between the sub-groove 5 and the circumferential main groove 3 is extremely lowered, the steering stability is lowered. Therefore, there is a problem that the number of sub-grooves contributing to sound absorption cannot be earned.

Therefore, in the pneumatic tire described in Patent Document 2, as shown in FIG. 4, the second sub-groove 31 including the axial groove portion 31 a and the circumferential groove portion 31 b that open in the circumferential main groove 24 is provided. It is conceivable to increase the number of sub-grooves 31 without lowering the rigidity of the ribs 28 by making the structure folded at an acute angle, and the noise level is actually reduced. However, even in this case, there is a problem that stone biting is likely to occur in the circumferential groove portion 31b of the sub-groove 31 and the bent portion forming an acute angle.
In particular, it has been found that when the circumferential groove is arranged at the center of the tread, stone biting is likely to occur. This is because the groove in the axial direction moves to open along with the deformation of stepping and kicking, but the groove in the circumferential direction is not deformed. When the sub-groove is provided in the tread central portion, the rigidity of the land portion sandwiching the groove portion in the circumferential direction is lowered, and there is a problem that the stone is likely to bite into the groove. In other words, locally stiff portions, such as the apex where the tread contact surface and the side wall of the secondary groove contact, are deformed by stone biting and absorb tire deformation due to stepping and kicking out. Stones are likely to remain. In particular, it was found that stones are likely to remain in the portion where the minor groove is bent at an acute angle.

  Note that the air column resonance is caused by the compressed air in the circumferential main groove that is regarded as an air column as described above, and this air column resonance phenomenon is likely to occur in the circumferential main groove in the center portion of the tread. In order to further reduce air column resonance in the circumferential main groove in the central portion of the tread, the present inventor can also provide the above-described secondary groove branched from the circumferential main groove in the central portion of the tread, particularly in a rib including the equator. I found it preferable. Furthermore, if a sub-groove enters the tread side portion, steering stability is lowered and uneven wear may occur. From such a viewpoint, the sub-groove is preferably provided in the tread central portion.

  Here, when a plurality of circumferential main grooves are provided in the tread, the tread is partitioned into a tread side portion and a tread central portion. Here, the tread central portion refers to a region sandwiched between a circumferential main groove adjacent to one tread end of the tread and a circumferential main groove adjacent to the other tread end. Moreover, the center rib mentioned later shall point out the rib containing the equator of a tire.

  Therefore, the object of the present invention is to solve the above-described problems, reduce air column resonance generated by the circumferential main groove without sacrificing excellent steering stability, and improve drainage, Another object of the present invention is to provide a pneumatic tire that improves stone biting properties.

Furthermore, in the tire of Patent Document 3, by combining rubbers with different hardnesses, mass productivity is reduced, and although it is advantageous for stability at a large steering angle, it improves the maneuverability at a small steering angle. Is not connected.
In addition, when the configuration of Patent Document 4 is used for a vehicle having a high center of gravity, the steering performance at a small steering angle is improved, but the rigidity of the block outside the equator is not sufficient, so that the steering performance at a large steering angle is poor. There was a problem that it was enough.

  Accordingly, another object of the present invention is to solve the above-mentioned problems, and in a vehicle such as a passenger car of a large number of passengers that has been increasing in recent years, good steering stability from a small steering angle to a large steering angle. It is in providing the pneumatic tire which shows.

The gist of the present invention is as follows.
(1) In a pneumatic tire that includes at least two circumferential main grooves in a tread of the tire, and ribs are defined at least in the center of the tread by the circumferential main grooves.
The rib sectioned in the tread central portion includes a circumferential groove portion extending along the tire equator direction, and an axial groove portion extending at an acute angle with respect to the circumferential groove portion from one end of the circumferential groove portion. Provided a minor groove,
At least one end of the sub-groove opens into the circumferential main groove;
At least one of the circumferential groove portion and the axial groove portion has a groove width that increases and a groove depth decreases toward a bent portion of the circumferential groove portion and the axial groove portion.
A pneumatic tire characterized by that.

“At least one of the circumferential groove portion and the axial groove portion has a groove width that increases and a groove depth that decreases toward a bent portion between the circumferential groove portion and the axial groove portion. Is, for example, a case where the groove width gradually increases and the groove depth gradually decreases from at least one of the end portions of the sub-groove toward the bent portion, or the circumferential groove portion and the axial groove portion. The case where the groove width gradually increases and the groove depth gradually decreases from the central part in the longitudinal direction of at least one of the above to the bent part is included. Furthermore, it includes not only the case of gradual increase and decrease, but also the case of increase and decrease in stages.
Here, simply by making it shallow toward the tip, the land portion inside the acute angle of the bent portion, that is, the tip of the land portion partitioned at an acute angle by the groove wall of the circumferential groove portion and the groove wall of the axial groove portion The movement of the stone can be improved by restricting the movement of the part, but not only the volume of the groove can not be earned, but the cross-sectional area becomes extremely small as it wears, so the drainage performance deteriorates and the noise reduction effect Get smaller. Further, simply widening the groove width reduces the block rigidity and lowers the steering stability.
If this configuration is used only on one side of the bent sub-groove, there is an effect of suppressing the occurrence of stone biting. Although not shown, a sub-groove having a pattern with three or more bent portions may be used. Also, in the embodiment, the chamfered part enters from the middle of the groove depth, but it is combined with the groove depth in such a structure that the groove width is spread on the average even if it enters from the groove bottom or no chamfered part. If it is, the effect of this invention will be acquired.

(2) The groove width of at least one of the bent portion that is one end of the circumferential groove portion and the bent portion that is one end of the axial groove portion is 5.0 mm or more and 12 mm or less,
The groove width of the other end of the circumferential groove portion and the other end of the axial groove portion is 1 mm or more and 2 mm or less,
The groove depth of at least one of the bent portion that is one end of the circumferential groove portion and the bent portion that is one end of the axial groove portion is 0.5 mm or more and 2 mm or less,
The groove depth of the other end of the circumferential groove portion and the other end of the axial groove portion is 5.0 mm or more and 6.5 mm or less.
The pneumatic tire according to (1) above, wherein

  Here, the groove width refers to the width of the opening including the chamfered portion when the sub-groove has a chamfered portion.

(3) The circumferential groove portion of the sub-groove has a chamfered portion that is inclined with respect to the surface of the tread on at least one side wall of both side walls defining the groove portion. Pneumatic tire described in 2.

(4) The pneumatic tire according to (3), wherein a chamfered portion provided on a side wall of a circumferential groove portion of the sub groove has an inclination angle with respect to the surface of the tread in a range of 20 degrees to 60 degrees.

(5) In a pneumatic tire having at least two circumferential main grooves in a tread of the tire and having ribs at least at the center of the tread in the circumferential main grooves,
In the cross section of the tire in the width direction, with the tire equator as a boundary, the maximum width Wout of the region that becomes the vehicle outer side when the vehicle is mounted is longer than the maximum width Win of the region that becomes the vehicle inner side when the vehicle is mounted,
The center width of the center rib including the tire equator is the vehicle outside when the vehicle is mounted from the tire equator,
The central rib is provided with a secondary groove that opens to the circumferential main groove on the vehicle outer side among the circumferential main grooves that define the central rib,
The secondary groove does not cross the tire equator of the central rib, and forms a continuous portion in the central rib.
A pneumatic tire characterized by that.

  In addition, the said continuous part is an area | region which does not contain the subgroove of a center rib, and means that a land part is continuing. This continuous part may include sipes.

(6) A secondary groove installed in the central rib includes a circumferential groove portion extending along the tire equator direction, and an axial direction extending by bending at an acute angle from one end of the circumferential groove portion with respect to the circumferential groove portion. Including a groove portion,
At least one of the circumferential groove portion and the axial groove portion has a groove width that increases and a groove depth decreases toward a bent portion of the circumferential groove portion and the axial groove portion.
The pneumatic tire according to (5) above, wherein

(7) The axial groove portion opens in a circumferential main groove, and the circumferential groove portion terminates in a central rib,
The distance between the end of the center rib on the vehicle inner side when the vehicle is mounted and the tire equator is 15% or more of the width of the center rib.
The pneumatic tire as described in (5) or (6) above, wherein

(8) The pneumatic tire according to any one of (5) to (7), wherein the center of the width of the continuous portion of the central rib is on the vehicle inner side when the vehicle is mounted with respect to the tire equator. .

(9) The pneumatic tire according to any one of (5) to (8), wherein the width of the central rib is 20% or more and 40% or less of the tread contact width.

  According to the present invention, in order to reduce the air column resonance generated by the circumferential main groove, the secondary groove having at least one end opened to the circumferential main groove is bent at an acute angle and provided at the center of the tread. Stone biting caused by bending can be avoided by increasing the groove width of the bent portion, which is an acute angle portion of the sub-groove, and decreasing the groove depth. Therefore, it is possible to provide a pneumatic tire with improved drainage and improved stone biting performance without sacrificing excellent handling stability.

  Further, in the cross section of the tire in the width direction, the maximum width length Wout of the region that becomes the vehicle outer side when the vehicle is mounted is longer than the maximum width Win of the region that becomes the vehicle inner side when the vehicle is mounted, and includes the tire equator. The center width of the central rib is the outer side of the vehicle when the vehicle is mounted from the tire equator, and the central rib is provided with a secondary groove that opens to the circumferential main groove on the vehicle outer side among the circumferential main grooves that define the central rib. With the configuration in which the groove does not divide the tire equator of the central rib, it is possible to provide a pneumatic tire that exhibits good steering stability from a small rudder angle to a large rudder angle when mounted on a vehicle having a high vehicle height.

Hereinafter, embodiments of the pneumatic tire of the present invention will be described in detail with reference to the drawings.
In addition, since the internal reinforcement structure of a tire is the same as that of a general radial tire, illustration is abbreviate | omitted.

1A is a development view of a tread pattern schematically showing an embodiment of the pneumatic tire of the present invention, FIG. 1B is a partially enlarged view of FIG. 1A, and FIG. ) Is a cross-sectional view taken along line AA in FIG.
As shown in FIG. 1A, the tire tread 1 is provided with two circumferential main grooves 2 and 3 extending along the tire equator C, which are paired with the tire equator C interposed therebetween. A central rib 4 is defined between 2 and 3. Further, a sub-groove 5 is provided in the central rib 4. The sub-groove 5 extends along the tire equator C from a circumferential groove portion 5C, and from one end of the circumferential groove portion 5C to be bent at an acute angle with respect to the circumferential main groove 3, and the circumferential main groove. 3, and an axial groove portion 5 </ b> W opening to 3. The circumferential groove portion 5C has a chamfered portion 5M described later.
Thus, by making the sub-groove 5 communicate with the circumferential main groove 3, the frequency of the air column resonance generated in the circumferential main groove can be dispersed as described above.
In addition to the sound absorbing effect, it is preferable to provide a large number of grooves having a certain length in the tread in consideration of drainage. Therefore, by arranging the auxiliary groove 5 while bending it at an acute angle, a large number of grooves can be arranged while securing the rigidity of the central rib 4 without dividing the central rib 4. In particular, since it is preferable to provide a groove in the central rib 4 having a high ground pressure, drainage and quietness can be improved by providing the sub-groove 5 as described above.
As described above, by providing the sub-groove 5 in the center portion of the tread, particularly the central rib 4, the frequency of the air column resonance generated in the circumferential main groove is dispersed and drainage performance is improved while maintaining good steering stability. There is an advantage that you can.

1B, the circumferential groove portion 5C is directed from the portion terminating in the central rib 4 toward the bent portion 5K between the circumferential groove portion 5C and the axial groove portion 5W. Thus, the groove width gradually increases and the groove depth gradually decreases. On the other hand, in this configuration, as described above, it is known that stone biting is unlikely to occur in the axial direction, and therefore the groove width and depth of the axial groove portion are not changed much.
Here, the groove width W _C of the circumferential groove portion 5C in the bending portion 5K, in the circumferential groove portion 5C, with respect to a line segment passing through the center of the groove width of including the chamfered portion 5M circumferential groove portion 5C, Of the intersections K ₁ and K ₂ between the groove wall of the circumferential groove portion 5C of the bent portion 5K and the groove wall of the axial groove portion 5W, the perpendicular to the line segment from the intersection K ₁ inside the acute angle is the circumferential groove portion. It refers to the distance to the point that intersects the 5C groove wall. Similarly, the groove width W _W of the axial groove portion 5W at the bent portion 5K, with respect to a line segment passing through the center of the groove width of the circumferential groove portion 5W, with respect to the line segment from acute inside the intersection K ₁ It refers to the distance to the point where the perpendicular intersects the groove wall of the axial groove portion 5W.

  In the example of FIG. 1, the circumferential groove portion 5C is an example in which the groove width is gradually increased toward the bent portion 5K and the groove depth is gradually decreased, but the circumferential groove portion 5C and the axial groove portion 5W. Both or only the axial groove portion 5W may gradually increase the groove width and gradually decrease the groove depth toward the bent portion 5K.

As described above, the axial groove portion 5W is bent at an acute angle at the sub-groove 5 that opens in the circumferential main groove 3 to be provided at the center of the tread, thereby reducing air column resonance generated by the circumferential main groove 3. It becomes possible.
In addition, when considering the sub-groove alone, the entire sub-groove needs to be grounded so that the sound wave can be reflected and absorbed, but even if it is folded at an acute angle, the whole Easy to ground. Therefore, the folded sub-groove is particularly suitable for a tire having a wide contact width and a low flatness ratio.
However, there arises a problem that stone biting occurs in the bent portion 5K of the sub-groove 5 that is bent at an acute angle. This is because, when the sub-groove 5 is bent at an acute angle, the land portion inside the acute angle of the bent portion 5K, that is, the land portion partitioned at an acute angle by the groove wall of the circumferential groove portion 5C and the groove wall of the axial groove portion 5W. This is because the rigidity of the tip portion of the steel becomes low and stone biting is likely to occur. Therefore, the generation of this stone biting is reduced by widening the groove width of the bent portion and decreasing the groove depth.

Further, the groove width of at least one of the bent portion 5K which is one end of the circumferential groove portion 5C and the bent portion 5K which is one end of the axial groove portion 5W is 5.0 mm or more and 12 mm or less, and the circumferential groove portion 5C. It is preferable that the groove width of the other end of the first and second axial grooves 5W is 1 to 2 mm.
This is because if the groove widths of the bent portions 5K are both less than 5.0 mm, the effect of reducing the occurrence of stone biting is low, and if it exceeds 12 mm, the rigidity of the central rib 4 decreases.
Further, the groove depth of at least one of the bent portion 5K which is one end of the circumferential groove portion 5C and the bent portion 5K which is one end of the axial groove portion 5W is 0.5 to 2 mm, and the circumferential groove portion 5C It is preferable that the groove depth of the other end of each of the first and second axial grooves 5W is 5.0 mm or more and 6.5 mm or less.
This is because when both the groove depths of the bent portions 5K are less than 0.5 mm, the groove cross-sectional area becomes small, and the air column resonance noise caused by the circumferential main groove 3 cannot be sufficiently reduced. This is particularly noticeable during wear. Moreover, when it exceeds 2 mm, the rigidity of a land part falls and steering stability falls.

  1A shows an example in which the sub-groove 5 is opened in the circumferential main groove 3, the sub-groove 5 may be opened in the circumferential main groove 2 side. Further, considering the dispersion effect of the air column resonance sound, it is preferable to provide the auxiliary grooves 5 for all the circumferential main grooves as much as possible.

Next, as illustrated in FIG. 1C, it is preferable that the circumferential groove portion 5 </ b> C of the sub-groove 5 has a tapered chamfered portion 5 </ b> M that is inclined with respect to the surface of the tread 1. . 1 shows an example in which the chamfered portion 5M is provided on the side wall on the axial groove portion 5W side, that is, the side wall opposite to the tire equator C, the chamfered portion 5M is provided on the side wall on the tire equator C side. Is preferred. This is because the tire equator C has a high contact pressure, and stone biting is likely to occur.
Here, the inclination angle θ is an angle formed by a line segment that passes through the opening edge P of the circumferential groove portion 5C of the sub-groove 5 and is parallel to the rotation axis of the tire and the chamfered portion 5M of the circumferential groove portion 5C.
When the secondary groove 5 is provided in the central rib 4 of the tread 1 of the tire, the rigidity is lowered particularly in the land portions on both sides of the circumferential groove portion 5C, and stone biting occurs in the circumferential groove portion 5C. Locally low rigidity parts, for example, the apex part where the tread contact surface and the side wall of the groove are in contact are deformed by biting the stone, and the tire deformation due to stepping and kicking out is absorbed, so the stone is in the groove. Easy to remain. Here, by providing the chamfered portion 5M in the circumferential groove portion 5C, it is possible to remove a portion where the rigidity is locally low and improve the stone biting property.
Further, by providing the chamfered portion 5M in the circumferential groove portion 5C, the cross-sectional area of the sub-groove 5 is increased, so that the volume of the sub-groove is increased and the frequency dispersion effect is increased. As well as improving drainage. In addition, since the ground contact area of the tread is reduced by providing the chamfered portion 5M in the circumferential groove portion 5C, the steering stability is in the direction of lowering, but the portion with low rigidity is removed and the area to be removed is small. Therefore, the impact on steering stability is considered to be small.
1C shows an example in which the groove bottom has a radius of curvature of r, the groove bottom may be flat. The groove depth d is a distance from the tread contact surface to the groove bottom.

  The inclination angle θ is preferably in the range of 20 to 60 degrees. Because if it is smaller than 20 degrees, the effect of improving the stone biting is small. On the other hand, when the angle is larger than 60 degrees, the land portion is largely cut off, and the rigidity of the rib is lowered, so that the steering stability is lowered.

FIG. 2A is a development view of a tread pattern schematically showing an embodiment of the pneumatic tire of the present invention, and FIG. 2B is a cross-sectional view taken along line BB in FIG. .
As shown in FIG. 2 (a), a circumferential groove portion 5C is formed on a rib 12 between two circumferential main grooves 2 and 11 extending along the tire equator C, which are paired across the tire equator C. A sub-groove 5 composed of _two axial groove portions 5W ₁ and 5W ₂ is provided. The secondary groove 5 is bent at an acute angle and is folded and ends in the rib 12. The circumferential main groove 2 is connected to the axial groove portion 5W _1, the axial groove portion 5W ₁ is connected to the circumferential groove portion 5C, the circumferential groove portion 5C is folded bent at an acute angle with the axial groove portion 5W ₂ Connected.
Circumferential groove portion 5C and an axial groove portion 5W ₂ groove width is gradually increased toward the bent portion 5K, the groove depth is gradually reduced. This structure improves the stone biting property of the bent portion 5K.
Further, as shown in FIG. 2 (b), the circumferential groove portion 5C on the side wall of the axial groove portion 5W ₂ side, has a tapered chamfered portion 5M inclined with respect to the surface of the tread, this structure Furthermore, the stone biting property is improved.

Further, as shown in FIG. 1, the width center M of the central rib 4 including the tire equator C is outside the vehicle when the vehicle is mounted from the tire equator C. The central rib 4 is provided with a sub-groove 5 that opens to the circumferential main groove 3 on the vehicle outer side of the circumferential main grooves 2 and 3, and the sub-groove 5 is arranged so as not to divide the tire equator C. ing.
With this configuration, it is possible to improve steering stability at a large steering angle. In other words, with respect to steering stability at a large steering angle, it is possible to obtain a large cornering force by being strong against axial force and having good grounding property, particularly on the outer side from the tire equator of the tread surface. It is essential. Therefore, it is desirable that the central rib is strong against the force in the width direction.
In this regard, FIG. 5 shows a tread pattern of a conventional tire. The central rib 4 and the land portion outside the vehicle from the central rib 4 are divided by the circumferential main groove 2, that is, 2 on the vehicle outer side. Since the main circumferential grooves 2 and 11 are provided, the steering stability at a large steering angle in a vehicle having a particularly high center of gravity is inferior.

  In addition, in the tire shown in FIG. 1, when the auxiliary groove 5 is not installed, when the load is applied to the outside from the tire equator C, the followability of the land portion is inferior. The cornering force cannot be obtained. For this reason, it is important to dispose the sub-groove and moderately reduce the rigidity of the land portion.

Next, the ride comfort of the vehicle will be described. The biggest external factor that degrades the ride comfort of a vehicle or reduces straight running stability, particularly steering stability at a small rudder angle, is the driving vehicle regardless of the vertical or horizontal direction of the vehicle. It is unevenness on the road surface that gives vibration. When this unevenness collides with the outer part of the vehicle when wearing the vehicle with the tire equator as the boundary and when it collides with the inner part, if the unevenness of the road surface is the same, In most passenger cars, the wheel mounting support portion (wheel hub surface) is offset, and the vehicle-mounted outer portion with a larger load share causes more vibration. For this reason, suppressing vibration input at the vehicle-mounted outer portion is effective in improving riding comfort. Therefore, if the road surface unevenness input can be substantially biased toward the inside of the vehicle, vibration input at the outside portion of the vehicle is suppressed, and as a result, riding comfort is improved.
As shown in FIG. 1, although the central rib 4 is divided by the auxiliary groove 5, the vehicle inner side when the vehicle is mounted is continuous, and the road surface unevenness input to the tire is substantially biased toward the vehicle mounting inner side. be able to. In particular, if the continuous portion can be arranged closer to the vehicle mounting inner side than the tire equator surface, the effect is further enhanced.
Further, by providing the auxiliary groove 4 in the vehicle mounting outer portion, it is difficult to transmit vibration. Therefore, the auxiliary groove 5 installed in the central rib 4 is installed outside 15% of the central rib 4, that is, the end of the central rib 4 on the vehicle inner side when the vehicle is mounted, the tire equator C, Is preferably 15% or more of the width of the central rib 4.
Furthermore, the rib-based block can increase the rigidity in the torsional direction on the tread surface. The continuous portion in the central rib 4 can further improve the steering stability at a small steering angle.

  In addition, as shown in FIG. 6, the pneumatic tire of the present invention has a maximum width Wout in a region outside the vehicle when the vehicle is mounted with the tire equator C as a boundary in the cross section in the width direction of the tire. It is important that it is longer than the maximum width Win of the region.

When the maximum width position of the tire is brought close to the tread portion, the radius of curvature of the curved portion from the tread portion to the sidewall portion in the tire cross section increases, and the rigidity against bending deformation of the portion can be increased. Therefore, it is important to apply such an action to the cross-sectional structure of the region that is inside the vehicle when the vehicle is mounted. Then, transmission of the steering force intended by the driver to the road surface can be easily achieved.
This is because most of the vehicles in recent years are given a negative camber. In such vehicles, when traveling straight or at a small steering angle, the load is mainly applied to the inside. Therefore, it is important to improve the steering stability of the small rudder angle by the above action.
Further, bringing the maximum width position closer to the tread portion means that SWHin is shortened.

  Due to the two synergistic effects of the tire cross-sectional structure and the tread pattern described above, even in a passenger car with a high center of gravity, it is possible to improve steering stability and riding comfort at a small steering angle region and a large steering angle.

Further, the sub-groove 5 installed in the central rib 4 extends at a sharp angle with respect to the circumferential groove portion 5C from the circumferential groove portion 5C extending along the tire equator direction and one end of the circumferential groove portion 5C. It is desirable to include the axial groove portion 5W.
In particular, the circumferential rib portion 5C is cut into an acute shape, and the central rib 4 appropriately follows the road surface even when there is a roll due to a large steering angle. However, even in that case, since the portion surrounded by the circumferential groove of the central rib 4 is connected to the continuous portion and maintains a certain degree of rigidity, a sufficient side force can be obtained while contacting the road surface. The body behavior is less likely to become unstable.
Further, at least one of the circumferential groove portion 5C and the axial groove portion 5W increases the groove width and decreases the groove depth toward the bent portion of the circumferential groove portion 5C and the axial groove portion 5W. It is important to maintain the rigidity of the central land portion 4 described above.
It is also desirable for measures against stone biting as described above.

As described above, in the case where the central rib 4 having a relatively large width is provided so as to be inward of the equator plane, it is natural that a circumferential groove or the like is brought inward in view of drainage. In addition, since the load on the outer side of the tire wearing by the roll at the large steering angle is not applied to the inner side, the problem of the followability is small. Considering them, it is preferable to arrange a rib-based block on the inside of the vehicle.
As described above, the rib-based block can increase the rigidity with respect to the torsional direction on the tread surface. Therefore, even in this portion, the steering stability at a small steering angle can be further improved.

First Example Next, the inventive tires 1 and 2 having the tread pattern shown in FIGS. 1 and 2, the conventional tire having the conventional tread pattern, and the comparative tires 1 to 3, both having a tire size of 205 / A prototype 55R16 radial tire for passenger cars was evaluated and the steering stability, drainage, noise reduction, and stone biting performance were evaluated and will be described below.
Table 1 shows the dimensions of the minor grooves of the inventive tires 1 and 2.
Invention example groove width W _c of the bent portion of the tire 1, in FIG. 1, a groove width in the cross-sectional view taken along the A'-A 'line. The groove width W _c of the central portion of Example tire 1 in FIG. 1, a groove width in the cross-sectional view taken along line A-A. Similarly, the groove width W _c of the bent portion of the tire 2 of the invention is the groove width in the cross-sectional view taken along the line B′-B ′ in FIG. 2, and the groove width W _c of the central portion in FIG. It is the groove width in sectional drawing which follows a BB line.
Since the groove width and groove depth of the axial groove portion of the inventive example tire 1 are constant, the numerical values are omitted.
The comparative tires 1 and 2 are the same as the inventive tires 1 and 2 except that the minor groove has a constant groove width and groove depth. The comparative example tire 3 is the same as the inventive example tire 1 except that the sub-groove gradually decreases toward the bent portion.

Conventional tires, invention tires 1 and 2 and comparative tires 1 to 3 were assembled on 16 × 7 J rims and mounted on the front and rear four wheels of a normal passenger car, respectively. At that time, 220 kPa was applied as the tire internal pressure for both front and rear. The load was equivalent to two passengers.
Using conventional tires, invention tires 1 and 2 and comparative tires 1 to 3, measurement of steering stability, measurement of drainage, measurement of white noise of air column resonance sound (silence) and stone biting Was measured.

<Measurement of steering stability>
The vehicle under the above-described conditions travels in a test course consisting of a circumferential circuit including a long straight portion and a handling curve with many gentle curves in a speed range from a low speed to about 150 km / h. The driver evaluated the feel of the steering wheel responsiveness to a maximum of 10 points. Inventive tire 1 was indexed as 0, and steering stability was evaluated, and the results are shown in Table 3.
Regarding the steering stability, all the inventive tires showed the results of maintaining good steering stability.

<Measurement of drainage>
The vehicle traveling under the above-mentioned conditions is accelerated while traveling in a straight road having a water depth of 10 mm, and the speed at which hydroplaning occurs is measured. The hydroplaning speed is defined by the following method. That is, when the actual travel distance is measured using five wheels and the measurement result is plotted together with the rotational speed, the speed corresponding to the rotational speed at which the slope changes suddenly is set as the hydroplaning generation speed. The average value measured three times was used as the average generation speed, and this average generation speed was indexed with the invention example tire 1 as 100. The drainage was evaluated, and the results are shown in Table 3.
In terms of drainage, all of the inventive tires showed an index of 99 or more, and showed the same or improved results as the conventional tires.

<Measurement of white noise in air column resonance>
Under the same conditions as the steering stability described above, the white noise of the air column resonance was evaluated by the driver's feeling. When the difference between the numerical values of the evaluation results is 1 or more, it is assumed that there is a significant difference.
The inventive tires all showed improved results.

<Measurement of stone biting property>
The number of stones remaining on the tires was measured after the stone biting mode running and the stone leaving mode running were continuously performed by the vehicle having the above-described conditions. Table 2 shows the conditions of the stone biting mode running and the stone leaving mode running, and Table 3 shows the results. In addition, the weather at the time of driving | running | working was fine and temperature was 12 degreeC.

  In Table 3, “small stone size” means a stone having a particle size of less than 5 mm, “medium” means a stone having a particle size of 5 mm or more and less than 10 mm, and “large” means a stone having a particle size of 10 mm or more.

  As for the stone biting property, the tire 1 of the invention has the groove width of the circumferential groove portion and the axial groove portion gradually increased toward the bent portion, the groove depth is gradually decreased, and the chamfered portion is further provided in the circumferential groove portion. No. 2 showed improvement in stone biting property as compared with the conventional tire and the comparative tire.

  According to the first embodiment, while maintaining good steering stability, the air column resonance sound generated by the circumferential main groove is made white noise to reduce the air column resonance sound, improve the drainage, and It has become possible to provide a pneumatic tire with improved biting characteristics.

Second Example Also, the tire 3 according to the invention has the pattern shown in FIG. 1 (a), and as shown in FIG. A tire was manufactured in which the maximum width Wout of the region outside the vehicle exceeded the maximum width Win of the region inside the vehicle when the vehicle was mounted.
The minor groove of the inventive example tire 3 is so that the distance from the end of the central rib 4 on the vehicle inner side to the tire equator C is 15% or more of the width of the central rib, that is, 15% of the width of the central rib 4. The width of the central rib was 26% of the tread ground contact width.
The continuous portion in the central rib is 17% of the rib width and is slightly offset from the equator.
Sipes are appropriately arranged on the central ribs, but these are strongly contacted by compression at the time of ground contact, and do not deteriorate the effect of maintaining the rigidity described above, and have nothing to do with the effect of the invention.
In addition, a rib-based block was placed further inside the central rib.
Further, although not shown as a comparative example tire 4, the circumferential groove portion of the auxiliary groove in FIG. 1A is eliminated, and the axial groove portion crosses the tire equator C, and is the same as that of the inventive example tire 3. A tire was prototyped.
Further, as a conventional tire, a tire similar to the inventive tire 3 was used except that it has a tread pattern shown in FIG.
Of the above tires, tires with a tire size of 195 65 R15 were mounted on Toyota Noah. The test vehicle was run on a test course by a professional test driver, and a feeling evaluation was performed.
The evaluation method of steering stability was performed as follows. As for steering stability at small steering angles, we conducted driving like a lane change on a highway, and evaluated the ease of handling and stability against disturbances. As for steering stability at a large rudder angle, slalom driving was carried out, and the ease of steering and the stability of the vehicle body were evaluated. Higher values indicate better steering stability.

  As shown in Table 4, it was found that the inventive tire 3 showed good steering stability at both the large steering angle and the small steering angle.

  According to the second embodiment, when the tire of the present invention is mounted on a vehicle having a high vehicle height, it is possible to provide a pneumatic tire that exhibits good steering stability from a small steering angle to a large steering angle. .

  As described above, while maintaining good steering stability, the air column resonance generated by the circumferential main groove is made white noise to reduce the air column resonance, improve drainage, and improve the stone bite. It has become possible to provide a pneumatic tire that is improved and exhibits good steering stability from a small steering angle to a large steering angle.

(A) is the development of the tread pattern which shows typically the embodiment of the pneumatic tire of the present invention, (b) is the elements on larger scale of Drawing 1 (a), and (c) is Drawing 1 (a) It is sectional drawing which follows the AA line in FIG. (A) shows the development view of the tread pattern of the inventive tire of the present invention, and (b) shows a cross-sectional view along the line BB in FIG. The expanded view of the tread pattern of the pneumatic tire of a prior art is shown. The expanded view of the tread pattern of the pneumatic tire of a prior art is shown. The expanded view of the tread pattern of the pneumatic tire of a prior art is shown. It is a figure which shows the cross section of the width direction of the tire of this invention.

Explanation of symbols

1 tread 2,3,6 circumferential main groove 4 center rib 5,7,8,9,10 sub-groove 12 rib 15A, 15B sipe 5C circumferential groove portion _5W, 5W _1, 5W ₂ axial grooves portion 5M chamfer C tire equator P opening edge

Claims (9)

In a pneumatic tire having at least two circumferential main grooves on a tread of the tire and having ribs at least at the center of the tread in the circumferential main grooves,
The rib sectioned in the tread central portion includes a circumferential groove portion extending along the tire equator direction, and an axial groove portion extending at an acute angle with respect to the circumferential groove portion from one end of the circumferential groove portion. Provided a minor groove,
At least one end of the sub-groove opens into the circumferential main groove;
At least one of the circumferential groove portion and the axial groove portion has a groove width that increases and a groove depth decreases toward a bent portion of the circumferential groove portion and the axial groove portion.
A pneumatic tire characterized by that. The groove width of at least one of the bent portion that is one end of the circumferential groove portion and the bent portion that is one end of the axial groove portion is 5.0 mm or more and 12 mm or less,
The groove width of the other end of the circumferential groove portion and the other end of the axial groove portion is 1 mm or more and 2 mm or less,
The groove depth of at least one of the bent portion that is one end of the circumferential groove portion and the bent portion that is one end of the axial groove portion is 0.5 mm or more and 2 mm or less,
The groove depth of the other end of the circumferential groove portion and the other end of the axial groove portion is 5.0 mm or more and 6.5 mm or less.
The pneumatic tire according to claim 1.   3. The pneumatic tire according to claim 1, wherein the circumferential groove portion of the sub-groove has a chamfered portion inclined with respect to the surface of the tread on at least one side wall of both side walls defining the groove portion. .   The pneumatic tire according to claim 3, wherein an inclination angle of a chamfered portion provided on a side wall of a circumferential groove portion of the sub groove with respect to the surface of the tread is in a range of 20 degrees to 60 degrees. In a pneumatic tire having at least two circumferential main grooves on a tread of the tire and having ribs at least at the center of the tread in the circumferential main grooves,
In the cross section of the tire in the width direction, with the tire equator as a boundary, the maximum width Wout of the region that becomes the vehicle outer side when the vehicle is mounted is longer than the maximum width Win of the region that becomes the vehicle inner side when the vehicle is mounted,
The center width of the center rib including the tire equator is the vehicle outside when the vehicle is mounted from the tire equator,
The central rib is provided with a secondary groove that opens to the circumferential main groove on the vehicle outer side among the circumferential main grooves that define the central rib,
The secondary groove does not cross the tire equator of the central rib, and forms a continuous portion in the central rib.
A pneumatic tire characterized by that. A sub-groove installed in the central rib includes a circumferential groove portion extending along the tire equator direction, and an axial groove portion extending from one end of the circumferential groove portion by bending at an acute angle with respect to the circumferential groove portion. Including
At least one of the circumferential groove portion and the axial groove portion has a groove width that increases and a groove depth decreases toward a bent portion of the circumferential groove portion and the axial groove portion.
The pneumatic tire according to claim 5. The axial groove portion opens into a circumferential main groove, the circumferential groove portion terminates in a central rib,
The distance between the end of the center rib on the vehicle inner side when the vehicle is mounted and the tire equator is 15% or more of the width of the center rib.
The pneumatic tire according to claim 5 or 6, characterized in that.   The pneumatic tire according to any one of claims 5 to 7, wherein a center of the width of the continuous portion of the central rib is on the vehicle inner side when the vehicle is mounted with respect to the tire equator.   The pneumatic tire according to any one of claims 5 to 8, wherein a width of the central rib is 20% or more and 40% or less of a tread contact width.

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